Most types of vehicle body structures include a centrally-formed tunnel or passage that extends along the long axis of the vehicle generally from the vehicle's firewall rearward to a point behind the second set or row of seats. Various components, such as the transmission, the drive shaft (in the case of the rear wheel drive vehicle), or conduits may extend through the tunnel.
While typically being a necessary component in the modern vehicle, the tunnel unfortunately too often plays a role in the increase of one or more of noise, vibration or harshness (NVH) within the vehicle. To minimize the NVH a tunnel brace is commonly provided between the opposing floor panels adjacent the tunnel such that the tunnel brace is fitted perpendicular to the long axis of the vehicle.
A typical tunnel brace arrangement according to current design is generally illustrated as 10 in FIG. 1. The tunnel brace arrangement 10 includes a tunnel brace 12 provided to bridge the gap defined by a tunnel 14. As is known in the art, the tunnel 14 is formed between a first floor pan 16 and a second floor pan 18. The tunnel brace 12 is attached at one end to the first floor pan 16 and at the other end to the second floor pan 18. A first supporting cross-member 20 is integrally attached to the first floor pan 16 while a second supporting cross-member 22 is integrally attached to the second floor pan 18.
The tunnel brace 12 is fastened by several nut-and-bolt fasteners or by welding to the first floor pan 16 and to the second floor pan 18. FIG. 2 illustrates a bottom view of an example of a known tunnel brace 12 having two fastener holes 24, 24′ for receiving conventional bolts (not shown).
The addition of the tunnel brace results in increased torsion stiffness and a consequent reduction of NVH. While generally providing a satisfactory result in the reduction of vehicle NVH, the inclusion of the tunnel brace introduces another challenge to designers which is a possible negative affect in the event of a side impact. Since the main purpose of vehicle tunnel brace is to improve vehicle torsion stiffness and thus reduce NVH, the reacting forces on the tunnel brace are vertical whereas side impact forces acting on the tunnel brace are lateral.
In the event of a side-impacting collision, local deflection of the floor pans and their supporting structures is a common result. This local deflection often translates into injury to the occupant. Referring to the prior art arrangement of FIG. 1, the impact on the tunnel brace arrangement 10 following a side impact is shown. In this figure, the second floor pan 18 has become bent and the supporting cross-member 22 has become twisted, largely because of the resilience of the tunnel brace 12 which remains generally intact. Thus the damage caused by the side impact has remained local. Injury is often transmitted to the occupant because of the localized damage. Particularly, due to the stiffness added by the conventional tunnel brace, the vehicle tunnel does not deform efficiently, thus most the deflection of vehicle occurs at the crash side. The extra local crush of vehicle structure leads to severe contact between door trim and occupants at the crash side, thus risking occupant safety.
Side impact events involving automotive vehicles typically include the imposition of dynamic loading to the vehicle body sides. The side impact event imposes severe loading on the structural members of the body. This situation is complicated by the fact that many compact or mid-sized vehicles have low rocker heights that may pass below the bumper of an impacting vehicle, resulting in high door velocities.
Generally two classes of objects that impact the vehicle side are known. The first class includes other vehicles (including other cars, trucks and other moving objects) and the second class includes poles and pole-like objects, such as telephone poles, street signs, and trees. The former class of objects is usually wider than the latter class of objects, and thus the localized damage caused by the pole or pole-like object may create greater localized damage than that caused by the vehicle.
Thus the vehicle tunnel brace may play a role in occupant injury in a side or oblique pole impact. The automotive industry is aware of this situation and has thus established standards (FMVSS 214 in the US and ECE 95 in Europe) specifying safety requirements for pole or pole-like vehicle impacts. In order to more effectively meet and exceed such requirements it is desirable to provide an alternate arrangement for the tunnel brace as is currently used.
Accordingly, as in so many areas of vehicle technology, there is room in the art of tunnel brace design for an alternative arrangement.